Zombies Ate My Nieghbors

The amount of nostalgia I have for this game is borderline ridiculous. I rented it for the SNES when I was somewhere between six and eight, and I can still remember playing it pretty vividly, how cool everything about it was and how hard (at the time) it seemed to be.
I seriously probably died and had to repeat the first few levels so many times that, when I booted it up on an emulator a few months ago, I remembered pretty much everything about the first five levels.
You take the place of one of two teens (or both, in multiplayer) who are all that stand between the teeming hordes of zombies, werewolves, and b-movie monsters, and, well, your hapless neighbors.
Scattered around each level are a few of your cowering co-humans who've got to rescue before they get eaten up. Saving more earns you more points and a few extra lives, which can come quite in handy as this game is pretty hard.

'Zombies Ate My Neighbors' has become a cult classic in its own right, which isn't a surprise as it's full of clever little twists and nods and unexpected happenings. Weapons range from your standard water gun, to bazookas and silverware and even a weed whacker.
For bosses, you'll fight giant babies and possessed toys and all sorts of weirdness.
This game was actually re-released and slightly remastered for the Wii a little while ago, so if you have one it would be worth checking out, especially since it's co-op.
Because of it's popularity, it's also pretty easy to find a decent ROM of it.